The present invention relates to switching devices used to interrupt one or more circuit connections, particularly power line conductors in response to signals from ground fault protection circuitry. The invention provides a resettable switching device that can be reset only when certain preconditions are satisfied.
Ground fault protective devices used in a permanently connected installation (such as a wall box) require only that the hot or "live" conductor be interrupted in the event of a ground fault. However, in portable power equipment employing ground fault protective devices the neutral conductor could become disconnected due to rough handling, etc. and the protective circuit deenergized. A fault current between the hot conductor and ground would then go undetected through loss of the neutral conductor. This possibility has prompted U.L. to require that non-permanently connected ground fault protective equipment in this country include means for detecting an open neutral conductor.
The means usually employed includes a separate device such as a self-latching relay that will maintain load circuit continuity only so long as both hot and neutral conductors are connected. These relay devices tend to be bulky and expensive and awkward for use with portable equipment.
Other known resettable circuit interrupt devices typically utilize complicated mechanisms to set and reset the contacts. These mechanical arrangements have tended to be complex and intricate because one necessary safety requirement is that the device must not be capable of being reset unless a safe circuit is present. This complexity, however, drives up manufacturing costs and reduces reliability.
Accordingly, the need exists for a resettable circuit interrupter that is simple in design, avoids complex mechanisms for actuating circuit connection and thereby provides a low cost yet reliable means for setting and resetting the device.